Goward et al U.S. Pat. No. 4,248,940 is directed to a process for the coating of nickel-based superalloys with a graded thermal barrier coating of multiple layers, each having an increased proportion of ceramic materials. The concentration of gradient facilitates smooth transition from a bond material having small quantities of ceramic material to a top layer thermal barrier coating which is predominantly of ceramic material.
Gedwill et al U.S. Pat. No. 4,451,496 is concerned with a coating system comprising a metal/ceramic cermet applied to a substrate with a metallic layer subsequently applied to the cermet layer.
Naik U.S. Pat. No. 4,714,624 describes a method of applying a metal coating system comprising two metallic layers. The outer layer is an MCrAlY coating, and the inner layer is an aluminide coating.
Vine et al U.S. Pat. No. 4,861,618 is concerned with a specific thermal barrier coating for superalloys comprising a specific NiCoCrAlY composition for the metallic layer and a specific ZrO.sub.2 --Y.sub.2 O.sub.3.
Gupta U.S. Pat. No. 4,897,315 discloses an aluminized MCrAlY coating. Merz et al U.S. Pat. No. 5,032,469 describes a metallic coating of stainless steel plus titanium, zirconium, hafnium, niobium, tantalum, molybdenum and/or tungsten.